CCT System Operation & Monitoring 3 — Questions and Answers
Question 1: During a Casper preventive maintenance cycle, a technician notices that the dry pump exhaust pressure is 15% higher than the baseline recorded three months ago. This MOST likely indicates:
- Improved pump efficiency
- Partial blockage in the exhaust line or scrubber (Correct answer)
- Lower process gas usage
- Normal seasonal variation
Correct answer: Partial blockage in the exhaust line or scrubber
Rising exhaust backpressure is a common sign of particulate buildup or condensate accumulation in the exhaust line or abatement system.
Question 2: When performing a Casper system leak check using a helium mass spectrometer, which method provides the most reliable results?
- Spray helium on external joints while monitoring the leak rate (Correct answer)
- Fill the chamber with helium and monitor from outside
- Run the system at atmospheric pressure and measure
- Check only flange connections over 2 inches in diameter
Correct answer: Spray helium on external joints while monitoring the leak rate
Spraying helium externally on joints while monitoring the spectrometer response allows precise localization of leak points.
Question 3: A Casper system's chiller setpoint is 20°C but the chiller outlet temperature reads 23°C during process. What is the MOST likely cause?
- Refrigerant overcharge
- Insufficient coolant flow or chiller heat load exceeded (Correct answer)
- Chiller operating in heating mode
- Incorrect temperature units configured
Correct answer: Insufficient coolant flow or chiller heat load exceeded
When the outlet temperature exceeds setpoint, the chiller is typically unable to reject enough heat, often due to low flow or an excessive thermal load.
Question 4: In a Casper system, the electrostatic chuck (ESC) clamp voltage is applied but wafer lift-off after process shows the wafer is 'stuck.' What parameter should the technician check in the process log?
- RF generator frequency
- ESC de-chuck voltage ramp and dwell time (Correct answer)
- Chamber base pressure before process
- MFC calibration date
Correct answer: ESC de-chuck voltage ramp and dwell time
Insufficient de-chuck voltage duration or ramp profile is a common reason wafers remain adhered to the ESC after process completion.
Question 5: A Casper technician reviews the SPC (Statistical Process Control) chart for etch rate and finds the last 8 consecutive points are all below the center line. This pattern indicates:
- Random process variation within control limits
- A systematic process shift requiring investigation (Correct answer)
- The process is out of control and must be stopped immediately
- Normal batch-to-batch variation
Correct answer: A systematic process shift requiring investigation
Eight consecutive points on one side of the center line is a classic SPC run rule indicating a non-random systematic shift in the process.
Question 6: Which Casper system sensor would be MOST useful for detecting a plasma strike failure during process initiation?
- Thermocouple on the chamber wall
- RF delivered power and reflected power monitor (Correct answer)
- Coolant flow meter
- Exhaust gas analyzer
Correct answer: RF delivered power and reflected power monitor
A sudden spike in reflected power without a corresponding drop during ignition phase indicates the plasma failed to strike and ignite.
Question 7: A Casper system alarm log shows 'interlock violated: door open during pump sequence.' The SAFEST immediate response is:
- Override the interlock and continue pumping
- Stop the pump sequence and verify the door is fully secured before resuming (Correct answer)
- Ignore it if the door appears closed visually
- Increase pump speed to compensate for the potential leak
Correct answer: Stop the pump sequence and verify the door is fully secured before resuming
Interlocks protect both equipment and personnel; the correct response is always to clear the unsafe condition before resuming any automated sequence.
CCT System Operation & Monitoring 3
During a Casper preventive maintenance cycle, a technician notices that the dry pump exhaust pressure is 15% higher than the baseline recorded three months ago.
This MOST likely indicates: